Poly(arylene thioethers) (hereinafter may be abbreviated as "PATEs") represented by poly(phenylene sulfide) (hereinafter may be abbreviated as "PPS") are known as polymers which have a high melting point and are excellent in heat resistance and mechanical properties. In particular, a PATE obtained by subjecting an alkali metal sulfide and a dihalogen-substituted aromatic compound to polymerization under two-step heating in the presence of water in an amount specifically controlled in an organic amide solvent can be provided as a high-molecular weight polymer in the form of granules (U.S. Pat. No. 4,645,826; EP 166368).
However, PATEs commonly used involve problems of their insufficient compatibility with polymers of different kinds and poor adhesion properties to other materials such as metals. It has therefore been proposed to introduce various kinds of functional groups into PATE molecules so as to overcome these problems. PATEs with functional groups introduced thereinto can also be further converted into various modifications or derivatives by using the functional groups.
For example, Japanese Patent Application Laid-Open No. 305131/1988 has proposed a production process of a copolymer having functional groups, in which dihalogen-substituted aromatic carboxylic acid such as dichlorobenzoic acid or an alkali metal salt thereof, a dihalogen-substituted aromatic compound and an alkali metal sulfide are polymerized in the presence of a polar solvent substantially free of any water. However, this process can provide a copolymer only in the form of powder and hence involves problems of difficulties in separation and purification of the copolymer from a reaction system upon its production, and of deterioration in weighability and handling properties of the copolymer and of environmental worsening due to flying of the fine powder upon its forming or molding and processing. In addition, it is difficult for such a process to provide any polymer having a sufficiently high molecular weight.
Japanese Patent Application Laid-Open No. 7249/1986 discloses a process for the production of a PATE containing at least one functional end group, in which a PATE with disulfide introduced into its main chain is prepared and the resulting PATE is then reacted with a reducing agent in the presence of a monofunctional compound. However, it is difficult for this process to provide any polymer high in molecular weight because the cutting of molecular chain is conducted. The melting point of the resulting polymer is also somewhat low.
Japanese Patent Application Laid-Open No. 283763/1990 discloses a resin composition containing a modified PPS obtained by reacting a carboxylic anhydride with a poly(phenylene sulfide) resin. More specifically, this modification reaction is carried out by a process wherein PPS powder is dry-blended with the carboxylic anhydride, and the resultant blend is then melted and kneaded in an extruder controlled at 290.degree.-310.degree. C. and then pelletized. However, when the modified PPS obtained by this process is subjected to a melt-extracting treatment in a solvent such as N-methyl-2-pyrrolidone (hereinafter may be abbreviated as "NMP"), the carboxylic acid component contained in the polymer is lost. Therefore, it can not be said that the PPS is strongly bonded to the carboxylic anhydride.
Japanese Patent Application Laid-Open No. 18422/1992 discloses a process for the production of a PATE with carboxyl groups or carboxylic anhydride groups introduced thereinto, in which a PATE with constituent units consisting of aminobenzene introduced into its main chain is prepared and the resulting PATE is then reacted with a carboxylic acid halide. According to this process, a polymer having a relatively high molecular weight can be obtained. However, since functional groups are introduced into the main chain of the polymer, not on the terminals thereof, the crystallinity of the polymer is reduced, so that the polymer tends to lower its heat resistance.
As described above, it is desirable that when a PATE containing functional groups therein is to be formed or molded either by itself or in the form of a mixture with another polymer, it should be in the form of granules easy to handle, not in the form of powder. According to the conventionally-known processes, however, any resulting polymers tend to become finer as the contents of the functional groups in the polymers increase.
On the other hand, when a dihalogen-substituted aromatic carboxylic acid, a dihalogen-substituted aromatic compound and an alkali metal sulfide are reacted with one another in the presence of an alkaline earth metal compound, a PATE copolymer containing carboxyl groups or their metal salts therein can be produced (EP 494518; CA 2,056,332, which were prior applications filed by the present assignee). According to this process, a PATE copolymer containing functional groups can be obtained in the form of granules. However, the use of an alkaline earth metal compound is essential to this process. In addition, the resulting copolymer tends to have somewhat insufficient heat stability with respect to the functional groups contained therein.
Accordingly, if a granular PATE having a high molecular weight and containing functional groups, which are good in heat resistance, such as a carboxyl group, can be prepared by a simple process, the application fields of PATEs become advantageously wider.